[llgo] irgen: do not emit an extra terminator for panic thunks

[pcc]

Summary

Found with GoSmith.

[axw]

LGTM

llgo/trunk/irgen/builtins.go

func (fr *frame) callRecover(isDeferredRecover bool) *govalue {
   llv := fr.builder.CreatePHI(fr.types.ToLLVM(eface), "")
   llv.AddIncoming(
     []llvm.Value{llvm.ConstNull(llv.Type()), recovered},
     []llvm.BasicBlock{startbb, recoverbb},
   )
   return newValue(llv, eface)
 }
 
-func (fr *frame) callPanic(arg *govalue) {
+func (fr *frame) callPanic(arg *govalue, term bool) {
   fr.runtime.panic.call(fr, arg.value)
+  if term {
     fr.builder.CreateUnreachable()
   }
+}

llgo/trunk/irgen/ssa.go

case *ssa.Next:
     if instr.IsString {
       fr.tuples[instr] = fr.stringIterNext(iter)
     } else {
       fr.tuples[instr] = fr.mapIterNext(iter)
     }
 
   case *ssa.Panic:
     arg := fr.value(instr.X)
-    fr.callPanic(arg)
+    fr.callPanic(arg, true)
 
   case *ssa.Phi:
     typ := instr.Type()
     phi := fr.builder.CreatePHI(fr.llvmtypes.ToLLVM(typ), instr.Comment)
     fr.env[instr] = newValue(phi, typ)
     fr.phis = append(fr.phis, pendingPhi{instr, phi})
 
   case *ssa.Range:
case "print", "println":
     llargs := make([]*govalue, len(args))
     for i, arg := range args {
       llargs[i] = fr.value(arg)
     }
     fr.printValues(builtin.Name() == "println", llargs...)
     return nil
 
   case "panic":
-    fr.callPanic(fr.value(args[0]))
+    fr.callPanic(fr.value(args[0]), false)
     return nil
 
   case "recover":
     return []*govalue{fr.callRecover(false)}
 
   case "append":
     return []*govalue{fr.callAppend(fr.value(args[0]), fr.value(args[1]))}
 

llgo/trunk/test/irgen/go-panic.go

+// RUN: llgo -S -emit-llvm -o - %s | FileCheck %s
+
+package foo
+
+func F() {
+  // CHECK: call void @__go_panic
+  // CHECK-NEXT: ret void
+  // CHECK-NEXT: }
+  go panic("")
+}